Former US president Bill Clinton has been admitted to a California hospital with a mystery infection.

Mr Clinton’s spokesman confirmed his admission on Thursday (US time).

“On Tuesday evening, former president Bill Clinton was admitted to UCI Medical centre for treatment of a non-COVID infection,” Angel Urena said via Twitter on Thursday.

“He is on the mend, in good spirits, and incredibly thankful to the doctors, nurses and staff providing him with excellent care.”

The spokesman added to Reuters: “He’s up and about, joking and charming the hospital staff.”

CNN reports the former president was being treated for sepsis, which is unrelated to his previous heart problems or coronavirus. Sepsis is a potentially life-threatening condition that occurs when the body’s response to an infection damages its own tissues.

Mr Clinton had a heart operation in 2004 and a routine stent procedure in 2010.

He is reportedly in intensive care, mostly because it allows more privacy. Doctors treating him at the University of California’s Irvine Medical Centre say he is not on a breathing machine.

Mr Clinton went to the hospital after feeling fatigued and was diagnosed with an infection of the bloodstream that doctors believe started as a urinary tract infection, CNN reported, citing his doctors.

The former president’s physicians, Alpesh Amin and Lisa Bardack, said he was “admitted to the hospital for close monitoring and administered IV antibiotics and fluids”.

“He remains at the hospital for continuous monitoring,” they said in a statement. “After two days of treatment, his white blood cell count is trending down and he is responding to antibiotics well.”

They added: “We hope to have him go home soon.”

Mr Clinton, a Democrat who was president from 1993-2001, has had past health issues, including a 2004 quadruple bypass surgery and a 2010 procedure to open a blocked artery in his heart with two stents. CNN reported that his current hospital stay is not related to his heart issues.

The former Arkansas governor came to the White House by defeating an incumbent president, Republican George H.W. Bush, and served during a period of acute partisanship in Washington, a harbinger of the current bitter political state.

Mr Clinton won re-election in 1996 against long-time Republican Senator Bob Dole.

He endured bruising political battles with Republicans. He was impeached in 1998 by the Republican-led House of Representatives over his sexual relationship with White House intern Monica Lewinsky but remained in office when the Senate acquitted him in 1999.

He is known for a remarkable talent for connecting with people and an exceptional understanding of policy issues.

Mr Clinton morphed into a political husband after leaving office, when his wife Hillary Clinton was elected US senator from New York in 2000. She unsuccessfully sought the 2008 Democratic presidential nomination and won the party’s 2016 nomination before losing the election to Donald Trump.

-AAP